1. Field of the Invention
The invention relates to a battery with planar high temperature fuel cells.
2. Description of the Prior Art
A battery of this kind is known from a European patent application with the number 9581039.5 (=P.6678)--designated EP-A xy in the following. The cells of the battery comprise, in each case, an electrochemically active plate and a three-layer interconnector formed as an air heat exchanger. The middle layer of the interconnector consists of a plate which has substantially the same coefficient of thermal expansion as the electrochemically active plate; the sideward layers are made of metal sheets which are substantially thinner than the plate of the middle layer. The metal sheets are structured in the manner of a relief and securely connected to the middle plate via a large number of contact points. The sideward metal sheets are formed for a direct contact with the electrochemically active plate and the corresponding plate of an adjacent cell.
Due to the high operating temperature and due to the formation of metallic oxides at the surface of the interconnectors, alloys must be used which consist of at least 25% chromium and which form a chromium oxide protective layer. The use of aluminides, which could also be used at elevated temperatures, is out of the question since aluminium oxide is electrically non-conductive, in contrast to chromium oxide. However, the occurrence of chromium oxide is combined with the disadvantage that this compound displays a certain volatility at the operating temperatures of the fuel cells and thus deposits on the electrodes of the electrochemically active plates, which leads to an ageing of these plates, namely an ageing in the form of a continually decreasing efficiency. This problem can be countered by means of suitable coatings: for this, see EP-A 0 714 147 (=P.6651).